Threatened fishes of the world: Labeo seeberi Gilchrist & Thompson, 1911 (Cyprinidae)

Abstract

Common names: Clanwilliam sandfish (E), Clanwilliam-sandvis (Afrikaans). Conservation status: Critically endangered (1996 submission to IUCN), previously rare (Skelton 1987). Identification: A large Labeo species (attaining 55 cm SL, Gaigher 1973) with minute scales. D IV, 9–10; A III, 5; 77–90 scales in lateral line, 36–50 scales around caudal peduncle. Body slender with narrow caudal peduncle. Head smooth, snout subequal to postorbit, mouth with well-developed papillose lips and a single pair of barbels. Body colour olive-grey (Skelton 1993). Drawing by Penny Meakin (Skelton 1987). Distribution: Confined to the Olifants River system, Western Cape, South Africa. Abundance: Once widespread and abundant in the Olifants system. There has been a dramatic reduction in numbers and range in the last 20 years (Cape Nature Conservation [CNC] database). The only healthy population, in the Oorlogskloof River, represents less than 10% of the original distribution range; other populations comprise low numbers of primarily adult fish. Habitat and ecology: L. seeberi prefers pools and deep runs of larger rivers where it bottom feeds, primarily on algae and detritus (Van Rensburg 1966). Age and growth have not been studied but captive juveniles are known to attain 20 mm after 3 months. Reproduction: Spawns mainly in spring (Gaigher 1973) during upstream migrations (Jubb 1967). Maturity is reached at approximately 250 mm SL (Jubb 1967) and 2 kg captive females yield about 80000 eggs, indicative of an altricial life-history style. Threats: The principal threats are rapidly expanding agricultural production within the Olifants system and the introduction of alien predatory invasive fishes, such as Micropterus dolomieu and M. salmoides, and Lepomis macrochirus. The Olifants system experiences hot dry summers with winter rainfall and extensive summer irrigation is carried out for citrus crops. Two large storage dams were built for this purpose on the mainstream of the Olifants River between 1922 and 1933 followed by many small and large weirs on its main tributaries. The natural upstream spawning migrations of L. seeberi in the Olifants River were stopped by these barriers as fishways were not built. Recent surveys indicate that L. seeberi has become locally extinct above Clanwilliam Dam, despite once being the dominant of the three large indigenous cyprinids there (Gaigher 1973). Conservation action: CNC has undertaken regular surveys of the Olifants system since 1965 and has successfully cultured L. seeberi since 1994 for restocking in suitable natural habitats and in farm dams within its natural range. The conservation status of the species has been determined and published (Skelton 1987, 1993). The Clanwilliam sandfish is listed as ‘endangered’ by CNC’s ordinance, a classification which makes it an offence to remove captured fishes from rivers and dams. Conservation recommendations: The biology and ecology of L. seeberi need to be further studied so as to quantify the impact of habitat loss and fragmentation as well as predation by alien fishes on its survival. Captive culture must continue with an emphasis on establishing refuge populations in alien-free areas. The conservation authorities need to establish a conservancy on the Oorlogskloof River that links private land with the Oorlogskloof Nature Reserve. Remarks: The Clanwilliam sandfish is now the most threatened of the three large endemic migratory cyprinids of the Olifants River system and may be a particularly sensitive indicator of the overall health of this system.